Of orange vegetables and vitamins: Q&A with Sherry Tanumihardjo

August 23, 2014

Sherry Tanumihardjo is a CALS professor of nutritional sciences and director of the Undergraduate Certificate in Global Health, a popular new program that draws participants from majors all across campus. She has almost three decades of experience working with vitamin A, and her research team has conducted studies in the United States, Indonesia, South Africa, Ghana, Burkina Faso and Zambia. Tanumihardjo has acted as a consultant to many studies throughout the world to assist with study design and appropriate standardization. She is a strong advocate for the promotion of nutritionally enhanced staple foods, vegetables and fruits to enhance overall health and well-being.

Describe your work with orange vegetables.
I have worked for a number of years on carrots of many colors as well as on orange-flesh sweet potato and, more recently, orange maize. Basically we are trying to improve the vitamin A status of individuals by having them consume more orange fruits and vegetables in general.

Can you give us an idea of how you go about doing that?
For many years I have worked with carrot breeder Phil Simon in the Department of Horticulture. He was breeding carrots for more orange color. We did a series of studies in both an animal model and in humans, trying to look at the uptake and distribution of the carotenoids that give the vegetables their orange color—and the vitamin A that is made from the carotenoids. Then we moved on to orange vegetables in humans in Africa. I have worked with orange-flesh sweet potato in South Africa and with orange maize in Zambia.

Can you describe the connection between the color and the nutritional value?
There are three well-known precursors of vitamin A that are called pro-vitamin A carotenoids. Those are beta-cryptoxanthin, alpha-carotene and beta-carotene. Many of you may have heard of beta-carotene because it is one of the compounds found in many over-the-counter supplements. But those are also the compounds that give carrots and orange maize their bright orange color.

What happens if there is not enough vitamin A in the diet?
The most drastic thing that can happen is death. So we go around trying to get people to improve their vitamin A intake not only to prevent death—there are many steps before that happens, and one of them is blindness. Vitamin A is extremely important in vision and it also helps us ward off disease, so it’s a very important vitamin.

How did you get started in Africa?
It actually started very slowly. I used to be a consultant and I would fly back and forth to different countries to help them look at study design. The sweet potato study was funded by the International Potato Center. I helped them design the study, they did the school implementation—a feeding study—and then I helped them get the work published. My work with orange maize started in 2004 in collaboration with HarvestPlus, a project managed by the International Food Policy Research Institute. We started working with animal models and then progressed to full-fledged feeding trials, the latest of which we finished in 2012.

What were some of the challenges in your work in Africa?
The challenge is that feeding trials, if they’re going to show what we call efficacy, have to be highly controlled. So that means you have to keep the children for long periods of time and feed them all of the foods—and the foods need to be the same across the group except your test food. So in South Africa we fed orange-flesh sweet potato to half the children and white-flesh sweet potato to the other half. And then when we moved on to orange maize we did two studies. One study was similar to the sweet potato study where we fed white maize and orange maize. And then we did a second study where we had three groups, which got a little more complicated. We had white maize, orange maize and then white maize with a vitamin A supplement.

Another challenge is that all of the human work that I do involves blood—so we have to take blood from these children. Vitamin A in the human body is stored in the liver, and we use indirect markers of liver reserves of vitamin A that you can pick up from the blood.

Looking down the road what kind of goals do you have for your research?
We would like for people to have optimal health by having a diet that has not only all the nutrients you need but also some of the potential compounds that gear us toward optimal health. So it’s not just about fighting blindness anymore, but to see if we can get people into a new nutritional state where they are actually able to ward off diseases such as cancer.

What kind of progress have you made?
We have had significant progress with sweet potato. Most people in Africa used to eat white sweet potato, not the orange sweet potato we eat here in the United States. Many countries in Africa have now adapted the vines to be orange-flesh sweet potatoes. We think that’s a success story. Regarding orange maize, there are three lines of orange maize that have been released by the Zambian government. Currently orange maize is available to consumers. Right now it’s at a premium price, but hopefully with time the price will come down to the level of white maize.

How did you get interested in this line of work?
It chose me. It wasn’t something that I was looking for, but I was working with vitamin A and if you’re working with vitamin A and status assessment, it’s going to draw you to the countries that may have a history of vitamin A deficiency.

Can you talk a little more about the international nutritional programming you’ve been involved in?
Most of the work that I’ve done is to support biochemical labs. We have not done a lot of nutrition education on the ground, although that is a goal of mine, especially in Zambia. We have discovered that Zambians actually have really good sources of vitamin A in their daily diets, so we want to help them continue to eat the fruits and vegetables that are good sources of those phytonutrients and vitamins and minerals.

The other thing that I work on is isotope methods, which sounds a little scary!

What are isotope methods and what do they do?
We work with a compound called 13C. Typical carbon in the human body is 12C and radioactive carbon is 14C. We are working with the form of carbon that constitutes 1 percent of the human body. It’s perfectly safe to use, but it also has allowed me to work with the International Atomic Energy Agency. That’s the same agency that oversees radioactive bombs in different countries, so it’s kind of interesting that they have something called Atoms for Peace. And they actually received the Nobel Peace Prize one year based on the safe use of isotopes in nutrition.

I have worked in several countries trying to help them understand isotope methods and to apply isotope methods at the population level to inform public health policy. It’s a very technical method, but it can answer questions of public health significance.

So it’s a research tool. And what kinds of questions does it answer?
It is the most sensitive marker of liver reserves of vitamin A. Basically what we do is we give a dose of vitamin A that has a slightly higher amount of 13C than what’s found naturally in the environment, and then we can follow the uptake and the clearance of that 13C in the human body. And from that we can calculate total body stores of vitamin A—how much is in the whole body.

To conclude here, there’s an interesting story about your office and a more recent career development of yours—serving as director of the Undergraduate Certificate in Global Health, a program you helped develop and launch in 2011.
Yes. The Nutritional Sciences Building was originally a children’s hospital, and this particular office that I sit in sat idle for many, many years, used only for small committee meetings and things like that. When we received funding for the Undergraduate Certificate in Global Health, I looked in this office again and realized that it now fits my purpose. Originally it was the viewing room for children who had died from a variety of diseases, and the parents would sit in this room and mourn their lost child. I decided that this room fit my new mantra at the university, which is to empower undergrads, to mobilize them, to try to change the world. And while I’m sure we won’t have 100 percent participation, we’ve already had about 1,000 students go through the program.